This invention relates generally to drive assemblies for deep-well submersible pumps and particularly to a gearbox brake used in such drive assembly.
Submersible rotary pumps in down-hole locations are connected to the surface drive assembly by a tubing string which can be of the order of 4,000 feet in length. Such an arrangement is disclosed in U.S. Pat. No. 4,372,379 (Kulhanek et al.) by way of example.
The surface drive assembly includes an electric motor which drives the rotary pump through the medium of the tubing string. In the event that the rotary pump overheats, for example due to the lowering of the oil level, the pump can heat and seize up. When this happens, because of its extreme length, the tubing string can continue to be rotated by the electric motor resulting in the twisting of the string with a consequent build up of torsion forces in the string. When a rotational limit is reached the motor ceased to turn and at this point the torsion built up in the tubing string can act in reverse causing the string to unwind thereby reverse-rotating the motor drive shaft. The forces unleashed when such unwinding occurs can result in the destruction of the surface drive assembly and in extreme cases can causes drive pulleys to literally explode.
In addition to the above, the provision of braking systems for use in conjunction with drive assemblies presents the problem of tampering where the brake system is a separate system and therefore easily accessible as well as being susceptible to moisture penetration. These problems are particularly acute where, as here, the system must be left unattended for long periods of time.
Also adequate lubrication of the shaft bearings is a problem for gearboxes of the type under consideration.
Brakes of various kinds have ben used without solving the problem satisfactorily. The present invention solves the problem in a manner not disclosed in the known prior art.